Metal-Free Multi-Heteroatom-Doped Carbon Bifunctional Electrocatalysts Derived from a Covalent Triazine Polymer.

ABSTRACT

The construction of multi-heteroatom-doped metal-free carbon with a reversibly oxygen-involving electrocatalytic performance is highly desirable for rechargeable metal-air batteries. However, the conventional approach for doping heteroatoms into the carbon matrix remains a huge challenge owing to multistep postdoping procedures. Here, a self-templated carbonization strategy to prepare a nitrogen, phosphorus, and fluorine tri-doped carbon nanosphere (NPF-CNS) is developed, during which a heteroatom-enriched covalent triazine polymer serves as a "self-doping" precursor with C, N, P, and F elements simultaneously, avoiding the tedious and inefficient postdoping procedures. Introducing F enhances the electronic structure and surface wettability of the as-obtained catalyst, beneficial to improve the electrocatalytic performance. The optimized NPF-CNS catalyst exhibits a superb electrocatalytic oxygen reduction reaction (ORR) activity, long-term durability in pH-universal conditions as well as outstanding oxygen evolution reaction (OER) performance in an alkaline electrolyte. These superior ORR/OER bifunctional electrocatalytic activities are attributed to the predesigned heteroatom catalytic active sites and high specific surface areas of NPF-CNS. As a demonstration, a zinc-air battery using the NPF-CNS cathode displays a high peak power density of 144 mW cm-2 and great stability during 385 discharging/charging cycles, surpassing that of the commercial Pt/C catalyst.